This invention relates to blending of fluid materials, especially particulate material, and more particularly, but not exclusively, is concerned with apparatus to control blending of two or more homogeneous, particulate materials automatically to obtain a predetermined volumetric blending ratio of the constituent materials in the blended product.
It is known to the Assignee of the instant application to provide apparatus for treating a particulate material, the constituent particles of which are non-uniform size, in order to obtain at least one product which meets a desired particulate specification the apparatus comprising a classifier which separates the particulate material into a relatively coarse underflow fraction and a relatively fine overflow fraction, and which has control means for varying as required the flow of the underflow fraction from the classifier.
The Assignee of the instant application makes and sells in U.K. such an apparatus, under the product name "T-type Classifier". The principle on which this classifier functions is one of "hindered settling" and the construction of the apparatus is such that the rate at which underflow fraction is removed can be continuously varied to some extent while it is in operation without affecting the particulate specification of the underflow.
It is sometimes useful to blend together two or more products of different particulate specification in order to achieve a product specification demanded by a customer. One way of achieving such a blend would be to store in bins two or more different output fractions from classifiers and then draw from the bins whatever relative weights of material are required for the blend. However, it is one disadvantage of this technique that the bins are expensive and take up valuable space.
Where more than two constituent materials are to be blended, it is undesirable for blending to continue in the event that one of the constituent flows falls below a minimum flow required for blending. The resultant combination of the other constituent flows is unlikely to meet a specification and may be of little or no value in consequence. Thus, it would be a desirable feature of any blending apparatus to be able to halt all combining the constituent flows should any one flow become deficient. It would be particularly advantageous if the particulate specifications of the constituent flows could themselves be adjusted so that each is a saleable commodity in itself.